Final answer:
The signal word that usually indicates a problem in a passage is A) Because, as it introduces a reason or cause that can lead to a problem.
Step-by-step explanation:
The signal word that points to the problem in a passage helps readers identify where an issue or conflict is introduced. Among the options provided, A) Because typically serves as a signal word for problems.
It functions as a conjunction that introduces a cause or reason, which often leads to a problem discussed in the passage.
The other options, B) Exactly, C) Decided, and D) Only do not inherently suggest a problem being presented. When reading, signal words like 'because' can indicate the beginning of an explanation for a predicament, conflict, or issue that characters in a story, or subjects in a non-fiction text, may be facing.